The Android Smiley Parser, which is built into the OS, but not available via the API (license included below). You've probably seen these in the messaging app.

To use the parser you must initialize it first with SmileyParser.init(Context);. I tend to do this my (Singleton) Application's onCreate, but you can do so in your Activity's onCreate as well since the instance will not get re-created if it already exists. 

After the instance has been created, just call SmileyParser.getInstance().addSmileySpans(CharSequence);

Android License

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */